Field
The present invention relates to an optical module and, particularly, to an optical module incorporating a semiconductor optical device in which a semiconductor laser and an optical amplifier are monolithically integrated.
Background
As a light source in an optical fiber communication system such as a 10G-Ethernet passive optical network (10G-EPON), an optical module incorporating an electro-absorption optical modulator integrated DFB laser is used (see, for example, JP 64-77187 A). In the optical module, laser light emitted from the semiconductor laser is modulated with an optical modulator. In a case where a type of optical modulator which intermittently absorbs light is used for this modulation, the output of modulated light is as small as about 0 to 10 dBm and is thus insufficient as an output from an optical line terminal (OLT) light source for a PON. The modulated light is therefore amplified to about 16 dBm with a semiconductor optical amplifier monolithically integrated in a chip before the light is input to an optical fiber. The optical modulator and the optical amplifier are joined to each other by using a butt joint method, and an interface therebeween is a butt joint interface.
Parasitic oscillation light in Fabry-Perot modes is generated between the emission end surface of the optical amplifier and the butt joint interface. This parasitic oscillation light enters the semiconductor laser and disturbs a carrier concentration distribution in the substantially same wavelength semiconductor laser. The oscillation light spectral line width of the semiconductor laser is thereby increased, causing phase noise at the time of optical fiber transmission and, hence, degradation in transmission characteristics.